Phase-shifted distributed feedback type semiconductor laser device

Abstract

A semiconductor laser device has a periodic structure for distributively feeding back light. A waveguide for guiding light along the periodic structure is provided. A plurality of waveguide regions having a light confinement coefficient set to vary along the periodic structure and an equivalent amount of phase shift with respect to the phase of the periodic structure set to an integer multiple of π are provided. The total phase shifting amount of light by the waveguide is set to a value different from an integer multiple of π.

What is claimed is: 
     
       1. A distributed feedback type semiconductor laser device having a periodic structure for distributively feeding back light, an active layer sandwiched between clad layers, a waveguide for guiding the light along said periodic structure, and first and second electrodes for injecting current into said active layer, said laser device comprising: a structure for shifting the phase of the transmitted light by changing at least one of the width and thickness of the waveguide along the periodic structure; and   a plurality of waveguide regions in which the shifting amount of the phase of the transmitted light caused by the change of at least one of the width and thickness of the waveguide is substantially an integral multiple of π;   wherein the sum of the total phase shift of the transmitted light caused by the change of at least on of the width and thickness of the waveguide is substantially an odd number multiple of π/2.   
     
     
       2. A distributed feedback type semiconductor laser device according to claim 1, wherein the phase shift amount of the transmitted light caused by changing at least one of the width and thickness of said waveguide is substantially an integral multiple of π, and the phase shift amount of the transmitted light caused by shifting the phase at a diffraction grating is substantially an odd number multiple of π/2. 
     
     
       3. A distributed feedback type semiconductor laser device according to claim 1, wherein said waveguide has a width smaller in the central portion of a resonator than in the end portion of the resonator. 
     
     
       4. A semiconductor laser device according to claim 1, wherein said waveguide has a plurality of wave-guiding regions having different propagation constants.